In the era of competition, continuous improvement of process and procedure is a must. In the field of metal cutting, broaching has the positive advantage of being a most simple and highly productive modern machining process, necessary for the engineering industries where repeatable product quality is required.
In broaching, the material is removed by successive action of a number of cutting teeth incorporated in the broach, which can be defined as a long cutting tool having a series of transverse cutting edges arranged lengthwise, progressively increasing in size, used to Finish internal or external surfaces, such as circular, square, irregular holes, internal spline, key ways, teeth of internal gears, flat surface or various other types on contour in a work piece in a single pass.
The essential feature of a broaching operation is that there is no feed given to the tool. The tool (broach) is self-fed due to the gradual increment in the successive teeth during the rectilinear working movement between the tool and work piece. Therefore broaching has become the simplest of operations and the broaching machine is very simple to operate.
Productivity improvement of ten times or even more is achieved, as the speed of metal removal by broaching is vastly greater. Roughing, semi-finishing and finishing of the component is done just in one pass by broaching, and this pass is generally accomplished in seconds and in most of the cases even the clamping of job is not required, as the broaching operation itself provides a force on the component which act as a clamping force against the fixture. Therefore the operation may be completed in much shorter time.
The conventional machining operations on the milling, shaper, planer, slotting machine or on some other machine tool are quite lengthy and even the processes do not give uniform accuracy. Therefore broaching has given birth to a significantly superior and highly productive machining process requiring minimum manpower, extending its use in wide fields of applications with exceptional savings on machine and tooling cost. The accuracy achieved and the efficiency demonstrated in heavy production by broaching is unmatched by any other process. Therefore broaching is especially suitable, rather essential for the industries where high efficiency, high level of accuracy and heavy production is required.
Earlier the broaching operation was used for key-ways, square/hexagonal/ octagonal holes, splines and some other specific shapes where the broach was pulled through a hole to remove the metal by the axial force applied by the broaching machine to obtain the desired shape. Today, in the highly competitive market, broaching has found its numerous applications including external/surface broaching, helical broaching and profile broaching of various special/complicated shapes. The broaching process has become necessary for automobile, hand tool and other large production engineering industries for its following distinguished advantages over the other machining processes:
· 100 per cent uniform accuracy
· Various contours and complicated irregular shapes can be easily broached
· Production of broaching is exceptionally high hence most suitable for mass production
· Broached surfaces are highly accurate in size and shape hence close tolerances can he maintained
· Short cycle time with high accuracy
· Remarkably finished face
· Extremely economical
· Zero per cent rejection
· Expertise not needed, and
· The broaching process is not limited to only mass production; some broaching machines developed by Supertech Crane-Bel Group are even suitable for small lots or even pieces production.
There are various types of operation broaching, which can be broadly classified into four clauses:
1.Internal Pull Broaching
Pull broaching is carried on either horizontal or vertical internal broaching machines. These are suitable for various components and shapes and are especially suitable for higher material removal, where the broach length is very high. Some examples of pull broaching are given below:
1. Round Shapes
These are machined by broaches with annular or helical teeth. The engagement of teeth is normally higher (5 to 7) to prevent misalignment during the operation. For thin walled components special measures are taken in a structuring broach, so that the maximum load is kept lower. This major cause of deformation and its reduction will ensure uniformity in the final size of the bore after broaching.
2. Grooved Shapes
These are the most commonly used in machine tools, vehicles, agriculture machinery, where every fixed or sliding tarsal movements are to be transmitted. Broaches used for these shapes commence work in the round hole. A simple example of the grooved hole is a quick lever of motorcycle/scooter and plumbers fittings.
3. Splined Holes
Spline broaches are used to finish cut involute spline or straight-sided spline. A combination broach, with both spline and round teeth, can be used to decrease the eccentricity on the minor and major diameters of a spline. Normally the broaches used for the groove shapes commence work in a round hole in which they create grooves. Some examples of the grooved shapes spline are as follows:
4. Helical Grooved Shapes
Helical grooves are broached in certain auto parts, pinions of motorcycle, rifling of firearms, making helical lubrication channels and for the production of modular parts for programming equipments, etc. The helical grooves are formed by means of helical shaped broaches, whose cutting teeth are set in accordance with individual helical generatrixes. The distinct feature of helical broaching is that in addition to the transverse movement, a rotary movement is also required between the broach and the work piece. There are two alternative systems to achieve this double motion:
a. With special Helical Broaching Machine equipped with the rotating fixture
In this system the broach moves in linear and direction, the job go on rotating, hence a helical movement is obtained.
b. With Broach Rotating Guide
In this system standard vertical broaching machine is used to provide linear movement to broach and a special guide is provided to rotate the broach, which is equipped with the guide grooves.
5. Regular Square, or Polygonal Shapes
These are very commonly used for cycle parts, automobile components, hand tools and for matrixes used for forming heads for nuts, etc. The hole is made around to start with and the First teeth of the broach widen hole and centre it shapes. The successive cutting teeth of the broach remove the material of the corner of the square or polygonal shapes to produce the finally required shapes.
Broaching very frequently does key- way cutting in the bore. The rectangular broaches used for key way cutting have cutting edges on one side only and are guided in the guide bush equipped with a grooved way, which fits in the hole to be broached exactly and supports the broach during working. Special shapes various shapes are broached to meet the technological or commercial requirement like inner curved teeth of positive displacement pump, half round seating profile of automobile gear shifter inner track free wheels, conveyor links, roller bearing cage and gear pump bodies.
2.Push type Broaching
These broaches operate by the thrust imposed by the vertical push type broaching machines. These broaches have a terminal section, which is longer than the work piece to ensure a sufficient run-out travel, but do not have the pull end. Push type internal broaches are commonly used for finishing of holes, sizing, key-ways, grooving and precision work. An important example is finishing of hole in bushing. A push type internal broach is used to finish the bore of the bushing.
The broaches have three types of teeth:
1. Cutting teeth
2. Finishing teeth, and
3. Hemispherical bumishing teeth
Push type internal broaches can also be used in the particular cases where holes are not through but adequate recessing is there.
3.External Broaching or Surface Broaching
Broaching of external surface is used in a number of manufacturing processes as an improvement of milling. Broaches of this type are of special construction and hence they cannot be Fit in to general pattern. Some examples of external surfaces are pump, rotor, grooves, hexagonal nut shape on nipples, grooved pines, grooved shafts of electric motor, selector gears, pinion notches and drawing shafts for textile machines.
Surface broaches are used in number of manufacturing processes as an improvement on milling shapes or planning operation. Some examples of surface broaching are:
1. Hand tools
2. Teeth cutting in racks
3. Teeth cutting in hacksaw blades
4. Dovetail and square slide
5. Sector gears
6. Many more shapes in automobile and engineering industries
7. Half round and flat mating surfaces of connecting rods and caps
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|Posted : 8/13/2005|